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تسجيل مستخدم جديدBoyajians Star B: The co-moving stellar companion to KIC 8462852
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The light curve of KIC 8462852, a.k.a Boyajians Star, undergoes deep dips the origin of which remains unclear. A faint star $approx$2arcsec to the east was discovered in Keck/NIRC2 imaging in Boyajian et al. (2016), but its status as a binary, and possible contribution to the observed variability, was unclear. Here, we use three epochs of Keck/NIRC2 imaging, spanning five years, in JHK near-infrared bands to obtain 1-mas precision astrometry. We show that the two objects exhibit common proper motion, measure a relative velocity of $mu=0.14pm0.44$ mas yr$^{-1}$ ($mu=0.30pm0.93$ km s$^{-1}$) and conclude that they are a binary pair at $880pm10$ AU projected separation. There is marginal detection of possible orbital motion, but our astrometry is insufficient to characterize the orbit. We show that two other point sources are not associated with KIC 8462852. We recommend that attempts to model KIC 8462852 As light curve should revisit the possibility that the bound stellar companion may play a role in causing the irregular brightness variations, for example through disruption of the orbits of bodies around the primary due to long-term orbital evolution of the binary orbit.
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A faint star located 2 arcsec from KIC 8462852 was discovered in Keck 10 m adaptive optics imaging in the $JHK$ near-infrared (NIR) in 2014 by Boyajian et al. (2016). The closeness of the star to KIC 8462852 suggested the two could constitute a binar
y, which might have implications for the cause of the brightness dips seen by {it Kepler} (Boyajian et al. (2016) and in ground-based optical studies Boyajian et al. (2018). Here, NIR imaging in 2017 using the Mimir instrument resolved the pair and enabled measuring their separation. The faint star had moved $67 pm 7$ milliarcsec (mas) relative to KIC 8462852 since 2014. The relative proper motion of the faint star is $23.9 pm 2.6$ mas yr$^{-1}$, for a tangential velocity of $45 pm 5$ km s$^{-1}$ if it is at the same 390 pc distance as KIC 8462852. Circular velocity at the 750 AU current projected separation is $1.5$ km s$^{-1}$, hence the star pair cannot be bound.
Over the duration of the Kepler mission, KIC8462852 was observed to undergo irregularly shaped, aperiodic dips in flux of up to $sim 20$%. The dipping activity can last for between 5 and 80 days. We characterize the object with high-resolution spectr
oscopy, spectral energy distribution fitting, radial velocity measurements, high-resolution imaging, and Fourier analyses of the Kepler light curve. We determine that KIC8462852 is a typical main-sequence F3 V star that exhibits no significant IR excess, and has no very close interacting companions. In this paper, we describe various scenarios to explain the dipping events observed in the Kepler light curve. We confirm that the dipping signals in the data are not caused by any instrumental or data processing artifact, and thus are astrophysical in origin. We construct scenario-independent constraints on the size and location of a body in the system that is needed to reproduce the observations. We deliberate over several assorted stellar and circumstellar astrophysical scenarios, most of which have problems explaining the data in hand. By considering the observational constraints on dust clumps in orbit around a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet or planetesimal fragments, all of which are associated with a single previous break-up event, possibly caused by tidal disruption or thermal processing. The minimum total mass associated with these fragments likely exceeds $10^{-6}$~mearth, corresponding to an original rocky body of $>100$~km in diameter. We discuss the necessity of future observations to help interpret the system.
We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping beg
an in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named Elsie, Celeste, Skara Brae, and Angkor, which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term secular dimming, which may be caused by independent processes, or probe different regimes of a single process.
The star KIC 8462852 (Boyajians Star) displays both fast dips of up to 20% on time scales of days, plus long-term secular fading by up to 19% on time scales from a year to a century. We report on CCD photometry of KIC 8462852 from 2015.75 to 2018.18,
with 19,176 images making for 1,866 nightly magnitudes in BVRI. Our light curves show a continuing secular decline (by 0.023 +- 0.003 mags in the B-band) with three superposed dips with duration 120-180 days. This demonstrates that there is a continuum of dip durations from a day to a century, so that the secular fading is seen to be by the same physical mechanism as the short-duration Kepler dips. The BVRI light curves all have the same shape, with the slopes and amplitudes for VRI being systematically smaller than in the B-band by factors of 0.77 +- 0.05, 0.50 +- 0.05, and 0.31 +- 0.05. We rule out any hypothesis involving occultation of the primary star by any star, planet, solid body, or optically thick cloud. But these ratios are the same as that expected for ordinary extinction by dust clouds. This chromatic extinction implies dust particle sizes going down to ~0.1 micron, suggesting that this dust will be rapidly blown away by stellar radiation pressure, so the dust clouds must have formed within months. The modern infrared observations were taken at a time when there was at least 12.4% +- 1.3% dust coverage (as part of the secular dimming), and this is consistent with dimming originating in circumstellar dust.
We report ground-based spectrophotometry of KIC 8462852, during its first dimming events since the end of the Kepler mission. The dimmings show a clear colour-signature, and are deeper in visual blue wavelengths than in red ones. The flux loss wavele
ngth dependency can be described with an AA ngstrom absorption coefficient of $2.19pm0.45$, which is compatible with absorption by optically thin dust with particle sizes on the order of 0.0015 to 0.15 $mu$m. These particles would be smaller than is required to be resistant against blow-out by radiation pressure when close to the star. During occultation events, these particles must be replenished on time-scales of days. If dust is indeed the source of KIC 8462852s dimming events, deeper dimming events should show more neutral colours, as is expected from optically thick absorbers.
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